Heat development to develop a light-sensitive material by heating is known in the art, and either black-and-white images or color images can be formed by use of this. Further, a transfer type heat developable light-sensitive material, which transfers images obtained by heat developing from a light-sensitive material to an image receiving later, is also known in the art.
In general, these heat developable light-sensitive materials have, on a support, binder, light-sensitive silver halide emulsion, reducing agent, and when necessary, dye-donating material, organic silver salt and other photographic additives, according to a prescribed structure. In the transfer type heat developable light-sensitive material, there are known two types: in one type, a light-sensitive material itself has an image receiving layer to receive silver or dyes; in the other type, an image receiving member containing an image receiving layer to receive silver or dyes is provided separately from a light-sensitive material.
In the above heat developable light-sensitive material, a variety of photographic useful reagents are employed, particularly heat developing accelerators and antifoggants are used most often.
The heat developable light-sensitive material generally contains a large amount of reducing agent reactive to a silver halide emulsion, which is liable to cause fog or lower a maximum density in storing. As measures to prevent such problems, there have been proposed various antifoggants, antifogging techniques, heat developing accelerators and heat developing acceleration techniques. But many of them are not necessarily satisfactory.
For example, there is proposed to add an antifoggant capable of preventing fog effectively in a light-sensitive layer beforehand, in order to prevent fogging in the heat developing process. However, most of such antifoggants have problems that when used in an amount enough to exert a satisfactory antifogging effect, they are liable to depress the heat development caused by reducing agents and formation of diffusible dyes, or to be absorbed by a light-sensitive silver halide emulsion, desorb sensitizing dyes and thereby lower the sensitivity.
These problems are often observed in heterocyclic antifoggants having a mercapto group which is particularly effective to prevent fogging. To be more specifically, these problems are liable to occur, for example, in nitrogen-containing heterocyclic mercapto-type antifoggants disclosed in Japanese Pat. O.P.I. Pub. Nos. 111636/1984, 58438/1988, 167750/1989, 222256/1989, 44336/1990 and 21442/1990.
Further, compounds to accelerate heat developing are also proposed in a large number. Such compounds include, for example, bases and base-releasing-agents, pyridium-group-containing cationic compounds disclosed in Japanese Pat. O.P.I. Pub. No. 74547/1984, 1-phenyl-3-pyrazolidone and its derivatives disclosed in Japanese Pat. O.P.I. Pub. Nos. 177549/1984 and 178458/1984, acetylene type compounds disclosed in Japanese Pat. O.P.I. Pub. No. 72233/1986, cyclic amide compounds disclosed in Japanese Pat. O.P.I. Pub. No. 77049/1986, specific nitrogen-containing heterocyclic compounds disclosed in Japanese Pat. O.P.I. Pub. No. 236548/1986, a method to perform heat development in the presence of silver halide solvents disclosed in Japanese Pat. O.P.I. Pub. No. 283335/1987, hydrazine compounds disclosed in Japanese Pat. O.P.I. Pub. No. 254442/1988, thioether compounds or cyclic thioether compounds disclosed in Japanese Pat. O.P.I. Pub. Nos. 301033/1988 and 301034/1988. However, use of these heat developing accelerators has many restrictions in amount and method and does not necessarily produce satisfactory results, because fog is liable to occur when these are contained in a heat developable light-sensitive material in an amount large enough to produce a satisfactory accelerating effect.
As a means to diminish these defects attributable to antifoggants and heat developing accelerators, there have been already proposed methods to add an antifoggant and a heat developing accelerator in a heat developable light-sensitive material in the form of precursors.
Such antifoggant precursors are disclosed, for example, in Japanese Pat. O.P.I. Pub. Nos. 67851/1986, 124941/1986, 147249/1986, 184539/1986, 185743/1986, 185744/1986, 188540/1986, 267045/1986, 269143/1986, 269147/1986, 269148/1986, 18550/1987, 65035/1987, 291642/1987, 42447/1990, 64634/1990, 135440/1990 and 178650/1990.
Examples of such a heat developing accelerator precursor can be seen in Japanese Pat. O.P.I. Pub. Nos. 72232/1986, 159642/1986, 170741/1986, 178953/1987, 182738/1987, 145652/1989, and Japanese Pat. Appl. No. 10085/1990.
These antifoggant precursors and heat developing accelerator precursors, though partly diminish the above defects, are not necessarily effective enough.
In order to diminish further the above problems raised in preservation of heat developable light-sensitive materials, there has been attempted to add the above antifoggant and heat developing accelerator or their precursors in an image receiving material, which is used in combination with a heat developable light-sensitive material. In this case, the above defects do not come out even when a heat developable light-sensitive material is preserved under considerably hard conditions, but other problems arise from the addition of the above compounds in an image receiving material other than a heat developable light-sensitive material.
That is, a heavy uneven heat development often occurs, unless an image receiving material is timely superposed on a heat developable light-sensitive material when these antifoggants and heat developing accelerators are fed form the image receiving material to a light-sensitive layer of the heat developable light-sensitive material.
The problems attributable to heat developing accelerators and antifoggants are described in the above paragraphs. Other photographic useful reagents, such as toning agents, fluorescent whitening agents, antistain agents, are difficult to add in heat developable light-sensitive material's photographic structural layers such as light-sensitive layer and intermediate layer, because of their liability to exert adverse effects on a light-sensitive layer while a heat developable light-sensitive material is stored.